feat: add wallet connect/disconnect component with Freighter integration

[mitchellecm7]

Closes #2

Changes

• Created components/wallet-connect.tsx with connect, disconnect, error, and loading states
• Integrated Freighter API v6 for Stellar wallet connection
• Persists wallet address to localStorage
• Replaced manual wallet logic in navbar with the new WalletConnect component
• Desktop and mobile menus both use the same component

Testing

• Connect button renders when disconnected
• Disconnect clears state and localStorage
• Error handling for missing Freighter extension
• No visual regressions

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[mitchellecm7]

Updated implementation:

Fixed Freighter API usage to match project version (getAddress)
Improved error handling and connection flow
Ready for review 🙌